Detection and determination of specified additives in mineral insulating oils

IEC 60666:2010 provides methods concerning the detection and determination of specified additives in unused and used mineral insulating oils. The detection methods may be applied to assess whether or not a mineral insulating oil contains an additive as specified by the supplier. The determination methods are used for the quantitative determination of additives known to be present or previously detected by the appropriate detection method. The main changes with respect to the previous edition are listed below:
- a change in the title from "Detection and determination of specified anti-oxidant additives in insulating oils";
- new Annexes B and C which provide methods for the determination of two additives different from the anti-oxidants.

Détection et dosage d'additifs spécifiques présents dans les huiles minérales isolantes

La CEI 60666:2010 fournit des méthodes concernant la détection et le dosage d'additifs spécifiques dans les huiles minérales isolantes neuves et usagées. Les méthodes de détection peuvent être appliquées pour vérifier si une huile isolante minérale contient ou non un additif comme le déclare le fournisseur. Les méthodes de dosage sont utilisées pour le dosage quantitatif des additifs préalablement décelés par la méthode de détection appropriée. Les modifications principales par rapport à l'édition précédente sont les suivantes:
- un changement dans le titre de " Détection et dosage d'additifs antioxydants spécifiques présents dans les huiles isolantes ";
- les nouvelles Annexes B et C, qui donnent des méthodes pour la détermination de deux additifs différents de l'anti-oxydant.

General Information

Status
Published
Publication Date
25-Apr-2010
Current Stage
PPUB - Publication issued
Start Date
26-Apr-2010
Completion Date
26-Apr-2010
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IEC 60666
Edition 2.0 2010-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Detection and determination of specified additives in mineral insulating oils
Détection et dosage d’additifs spécifiques présents dans les huiles minérales
isolantes
IEC 60666:2010
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 60666
Edition 2.0 2010-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Detection and determination of specified additives in mineral insulating oils
Détection et dosage d’additifs spécifiques présents dans les huiles minérales
isolantes
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX
ICS 17.220.99, 29.040.10 ISBN 978-2-88910-244-0
® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 2 – 60666 © IEC:2010
CONTENTS

FOREWORD...........................................................................................................................4

INTRODUCTION.....................................................................................................................6

1 Scope...............................................................................................................................7

2 Normative references .......................................................................................................7

3 Methods for the determination of anti-oxidant additives ....................................................7

3.1 Determination of phenolic and amine-based antioxidants by infrared (IR)

spectrophotometry – Method A ................................................................................7

3.1.1 Introductory remark .....................................................................................7

3.1.2 Equipment, materials and solvents ..............................................................8

3.1.3 Sample preparation .....................................................................................8

3.1.4 Calibration...................................................................................................8

3.1.5 Analysis.......................................................................................................9

3.1.6 Calculation ..................................................................................................9

3.1.7 Precision ...................................................................................................10

3.1.8 Repeatability .............................................................................................10

3.1.9 Reproducibility...........................................................................................10

3.1.10 Report .......................................................................................................10

3.2 Determination of 2,6-di-tert-butyl-para-cresol by IR spectrophotometry –

Method B...............................................................................................................10

3.2.1 Calibration.................................................................................................11

3.2.2 Sample test – New or used oil ...................................................................11

3.2.3 Precision ...................................................................................................11

3.2.4 Repeatability .............................................................................................11

3.2.5 Reproducibility...........................................................................................11

3.2.6 Report .......................................................................................................12

3.3 Determination of 2,6-di-tert-butyl-para-cresol (DBPC) by high performance

liquid chromatography (HPLC)...............................................................................12

3.3.1 Introductory remark ...................................................................................12

3.3.2 Materials and equipment ...........................................................................12

3.3.3 Reagents and solvents ..............................................................................12

3.3.4 Solid-liquid extraction ................................................................................12

3.3.5 Analysis of the extract ...............................................................................12

3.3.6 Calculation ................................................................................................13

3.3.7 Precision ...................................................................................................13

3.3.8 Repeatability .............................................................................................13

3.3.9 Reproducibility...........................................................................................13

3.3.10 Report .......................................................................................................13

3.4 Determination of phenolic inhibitors by gas chromatography – Mass

spectrometry (GC-MS)...........................................................................................

3.4.1 Summary of method ..................................................................................14

3.4.2 Example of instrument parameters ............................................................14

3.4.3 GC accessories .........................................................................................14

3.4.4 Calibration standard solutions ...................................................................14

3.4.5 Internal standard solutions ........................................................................14

3.4.6 Preparation of samples and calibration standards......................................15

3.4.7 Analytical procedure ..................................................................................15

3.4.8 Calculation of results .................................................................................15

3.4.9 Precision ...................................................................................................16

---------------------- Page: 4 ----------------------
60666 © IEC:2010 – 3 –

3.4.10 Report .......................................................................................................16

Annex A (informative) Detection of anti-oxidant additives by thin layer chromatography

(TLC) ....................................................................................................................................17

Annex B (informative) Analysis method for determination of passivators in mineral oils

by high performance liquid chromatography (HPLC) .............................................................22

Annex C (informative) Determination of pour point depressants by gel permeation

chromatography....................................................................................................................30

Bibliography..........................................................................................................................32

Figure A.1 – Typical infrared spectrum to determine DBPC content ......................................19

Figure A.2 – Typical infrared spectrum with 0,3 % DBPC ......................................................20

Figure A.3 – Typical HPLC chromatogram to determine DBPC content .................................21

Figure B.1 – UV spectra of TTAA (in blue) and BTA (in red)..................................................26

Table B.1 – Examples of separation conditions .....................................................................26

Table B.2 – Repeatability......................................................................................................29

Table B.3 – Reproducibility ...................................................................................................29

---------------------- Page: 5 ----------------------
– 4 – 60666 © IEC:2010
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
DETECTION AND DETERMINATION OF SPECIFIED
ADDITIVES IN MINERAL INSULATING OILS
FOREWORD

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

all national electrotechnical committees (IEC National Committees). The object of IEC is to promote

international co-operation on all questions concerning standardization in the electrical and electronic fields. To

this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,

Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC

Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested

in the subject dealt with may participate in this preparatory work. International, governmental and non-

governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely

with the International Organization for Standardization (ISO) in accordance with conditions determined by

agreement between the two organizations.

2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international

consensus of opinion on the relevant subjects since each technical committee has representation from all

interested IEC National Committees.

3) IEC Publications have the form of recommendations for international use and are accepted by IEC National

Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC

Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any

misinterpretation by any end user.

4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications

transparently to the maximum extent possible in their national and regional publications. Any divergence

between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in

the latter.

5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity

assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any

services carried out by independent certification bodies.

6) All users should ensure that they have the latest edition of this publication.

7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and

members of its technical committees and IEC National Committees for any personal injury, property damage or

other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and

expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC

Publications.

8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is

indispensable for the correct application of this publication.

9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of

patent rights. IEC shall not be held responsible for identifying any or all such patent rights.

International Standard IEC 60666 has been prepared by IEC technical committee 10: Fluids

for electrotechnical applications.

This second edition cancels and replaces the first edition, published in 1979, and constitutes

a technical revision.
The main changes with respect to the previous edition are listed below:

– a change in the title from “Detection and determination of specified anti-oxidant

additives in insulating oils” to “Detection and determination of specified additives in

mineral insulating oils”. The previous edition only addressed the detection and

determination of anti-oxidant additives, with particular regard to the DBPC, phenolic

inhibitors and anthranilic acid;
– more advanced methods for the determination of such anti-oxidant additives;

– new Annexes B and C which provide methods for the determination of two additives

different from the anti-oxidants. In particular, Annex B contains a method for the

determination of the concentration in used and unused insulating mineral oils of

passivators of the family of derivatives of benzotriazole. Annex C contains a method

---------------------- Page: 6 ----------------------
60666 © IEC:2010 – 5 –

for the qualitative identification of pour point depressants used in some commercially

available paraffinic oils to improve their low temperature properties.
The text of this standard is based on the following documents:
FDIS Report on voting
10/803/FDIS 10/807/RVD

Full information on the voting for the approval of this standard can be found in the report on

voting indicated in the above table.

This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

The committee has decided that the contents of this publication will remain unchanged until

the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data

related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates

that it contains colours which are considered to be useful for the correct

understanding of its contents. Users should therefore print this document using a

colour printer.
---------------------- Page: 7 ----------------------
– 6 – 60666 © IEC:2010
INTRODUCTION
General caution, health, safety and environmental protection

This International Standard does not purport to address all the safety problems associated

with its use. It is the responsibility of the user of the standard to establish appropriate health

and safety practices and determine the applicability of regulatory limitations prior to use.

The mineral oils which are the subject of this standard should be handled with due regard to

personal hygiene. Direct contact with eyes may cause slight irritation. In the case of eye

contact, irrigation with copious quantities of clean running water should be carried out and

medical advice sought.

Some of the tests specified in this standard involve the use of processes that could lead to a

hazardous situation. Attention is drawn to the relevant standard for guidance.

This standard involves mineral oils, chemicals and used sample containers. The disposal of

these items should be carried out in accordance with current national legislation with regard

to the impact on the environment. Every precaution should be taken to prevent the release

into the environment of mineral oil.
---------------------- Page: 8 ----------------------
60666 © IEC:2010 – 7 –
DETECTION AND DETERMINATION OF SPECIFIED
ADDITIVES IN MINERAL INSULATING OILS
1 Scope

The methods described in this International Standard concern the detection and determination

of specified additives in unused and used mineral insulating oils.

The detection methods may be applied to assess whether or not a mineral insulating oil

contains an additive as specified by the supplier.

The determination methods are used for the quantitative determination of additives known to

be present or previously detected by the appropriate detection method.
2 Normative references

The following referenced documents are indispensable for the application of this document.

For dated references, only the edition cited applies. For undated references, the latest edition

of the referenced document (including any amendments) applies.

IEC 60296, Fluids for electrotechnical applications – Unused mineral insulating oils for

transformers and switchgear
IEC 60475, Method of sampling liquid dielectrics

ISO 5725 (all parts), Accuracy (trueness and precision) of measurement methods and results

3 Methods for the determination of anti-oxidant additives
3.1 Determination of phenolic and amine-based antioxidants by infrared (IR)
spectrophotometry – Method A
3.1.1 Introductory remark

This method determines the amount of 2,6-di-tert-butyl-para-cresol (DBPC) in unused and

used mineral oils by measurement of the infrared absorption at the (O–H) stretching

frequency of hindered phenols. It can also be used to determine the amount of 2,6-di-tert-

butyl-phenol (DBP), but does not discriminate between them.

The previous test method in the first edition of IEC 60666 described a procedure for the

determination of specific antioxidants using IR techniques. This test method was satisfactory

with new oils, where no oxidation by-products interfere with the antioxidant. However, this

method was less satisfactory for used oils because oxidation by-products may modify the IR

baseline, making the detection and quantification of the antioxidants difficult. To overcome

this problem, a procedure for preparing a reference oil to be used as a baseline was

described. Unfortunately, this procedure was difficult to perform, was time-consuming and did

not ensure that the new baseline matched adequately that of the oil to be analysed, because

the content of some components of the baseline oil and the analysed oil could be quite

different.

This new method describes a procedure for preparing reference, antioxidant-free oils by solid

phase extraction (SPE) using silica gel.
---------------------- Page: 9 ----------------------
– 8 – 60666 © IEC:2010
3.1.2 Equipment, materials and solvents
The following materials and reagents are used:

– FT-IR or double-beam IR spectrometer having matched 1 mm sodium chloride cells (other

materials are accepted provided they do not absorb IR radiation in the range 3 000 cm

to 3 800 cm );
– 5 ml or 10 ml round-bottom flasks;
– 5 ml or 10 ml beakers;
– rotary evaporator;
– silica gel cartridges (1 g or 2 g size is satisfactory);
– n-pentane, analytical grade.
3.1.3 Sample preparation

Into a beaker pour 1 g of the oil to be analysed for antioxidants, add 2 ml of analytical grade

n-pentane and mix thoroughly.

Filter the solution through a silica gel cartridge and recover the eluate in a round-bottom flask.

Evaporate the n-pentane in the rotary evaporator.

Take a portion large enough to completely fill one IR cell of the oil that remains in the flask, fill

one IR cell and put it on the reference beam of the spectrometer.

Fill a second IR cell with the oil to be analysed, which has not been submitted to the filtration

process, and insert it on the analytical beam of the spectrometer.
Record the IR spectrum as described in 3.1.5.
3.1.4 Calibration

Prepare standard calibration solutions by dissolving weighed amounts of DBP or DBPC

inhibitor in weighed amounts of antioxidant-free oil, prepared if necessary from the oil sample

under test using the procedure in 3.1.3 (larger cartridges and amounts of oil will be

necessary).
The maximum life of the standard solution shall be six months.

NOTE The calibration solutions may be prepared using an unused, inhibitor-free oil, provided the base oil is

known to be the same as that under test. The oil should be tested by this procedure to ensure that no inhibitor is

detectable. This alternative should not be used where the oil under test is heavily aged.

Prepare at least five calibration solutions, covering the range 0,02 % to 0,50 % inhibitor by

mass.

Intermediate standards may be prepared if necessary when the approximate concentration of

inhibitor in the sample is known.

The absorbance (at 3 650 cm for DBPC) of the calibration solutions is recorded as

described in 3.1.5 and a calibration curve of absorbance against per cent inhibitor content

produced. The calibration should be a straight line passing through the origin, according to

the Beer-Lambert law of absorption:
A = log = KCD
where
---------------------- Page: 10 ----------------------
60666 © IEC:2010 – 9 –
A is the absorbance;
I is the intensity of incident radiation;
I is the intensity of transmitted radiation;
K is the extinction coefficient (constant for (O-H) of DBPC);
C is the concentration of DBPC in percentage by mass;
D is the cell path-length.

Since K and D are constant for this determination, A is directly proportional to C.

3.1.5 Analysis
1. FT-IR instrument

Check the equipment. The quality tests should be performed according to the manufacturer’s

recommendations.
2. Double-beam IR spectrophotometer

Prepare two matched liquid cells with path-lengths of 1 mm and sodium chloride windows. Fill

both cells with the base oil and, with one cell in the sample beam and the other in the

reference beam of the spectrometer and check that the IR spectrum between 3 800 cm and

3 400 cm is a straight line. Record the percentage transmittance (95 % – 100 %).

Exchange the cells, i.e. transfer the cell in the sample beam to the reference beam and the

cell in the reference beam to the sample beam. Repeat the spectrum acquisition and again

ensure a straight line of approximately 95 % to 100 % transmittance is obtained.

If the above conditions are not obtained, clean and polish or reject windows that have an

absorbance in this region, and repeat the process until a matched pair of cells is obtained.

These are then used for all the determinations.
Test solutions
1. FT-IR instrument

Fill the cell with the oil to be analysed and record the IR spectrum (A) at the appropriate

wavelength. Repeat using the inhibitor-free reference oil and subtract this result from

spectrum A to produce a spectrum with a linear baseline.
2. Double-beam IR spectrophotometer.

Take a portion of the inhibitor-free reference oil in the flask, completely fill an IR cell and

place it in the path of the reference beam of the spectrometer. Completely fill a second IR cell

with the oil to be analysed and place it in the analytical beam of the spectrometer. Record the

–1 –1

IR spectrum at the appropriate wavelength (in the range 3 500 cm to 3700 cm for DBPC).

3.1.6 Calculation
Measurement of absorbance
1. FT-IR instrument

Record the absorbance at the position of maximum peak height for the sample and for the

inhibitor-free reference oil.
---------------------- Page: 11 ----------------------
– 10 – 60666 © IEC:2010

Subtract the reference oil spectrum from the sample oil spectrum and quantify the result by

reference to calibration curves.
2. Double-beam IR spectrophotometer (see Figure A.1)
–1 –1

Draw a base line as nearly as possible between 3 610 cm and 3 680 cm and record the

percentage transmittance (I ) at which the base line crosses the 3 650 cm line.

Record the percentage transmittance at the tip of the peak at 3 650 cm (I), then:

A = log
3 650 10
The percentage DBPC equivalent to A is read from the calibration graph.
3 650
Alternatively, automatic determination by the spectrometer may be used.
3.1.7 Precision

The repeatability and reproducibility limits were established in accordance with the ISO 5725

series.
3.1.8 Repeatability

The difference between successive test results obtained by the same operator with the same

apparatus under constant operating conditions on identical test material would, in the long run,

in the normal and correct operation of the test method, exceed the values shown below by

only 1 case in 20:

– unused and used oils – 15 %, which can be calculated as (x +x )/2 × 0,15, where x and

1 2 1
x are the results of the two replicates.

NOTE The repeatability values for oils only apply where the result is above 0,05 % DBPC in oil.

3.1.9 Reproducibility

The difference between two single and independent results obtained by different operators

working in different laboratories on identical test material would, in the long run, in the normal

and correct operation of the test method, exceed the values shown below by only 1 case in 20:

– unused oils: for DBPC concentrations ≤ 0,1 %, the reproducibility is 0,02 % – absolute

value;

– unused oils: for DBPC concentrations > 0,1 %, the reproducibility is 45 %, which can be

calculated as (x +x )/2 × 0,45, where x and x are the results of the two replicates;

1 2 1 2

– used oils – 45 %, which can be calculated as (x +x )/2 × 0,45, where x and x are the

1 2 1 2
results of the two replicates.

NOTE The reproducibility values for used oils only apply where the result is above 0,05 % DBPC in oil.

3.1.10 Report

Report the concentration of phenolic and amine-based antioxidants in % to the nearest

0,01 %.
3.2 Determination of 2,6-di-tert-butyl-para-cresol by IR spectrophotometry –
Method B

For routine analysis of oils in service, a procedure, modifying 3.1 by the following changes,

may be used.
---------------------- Page: 12 ----------------------
60666 © IEC:2010 – 11 –
3.2.1 Calibration

Prepare one liquid cell with a path length of 0,2 mm and equipped with sodium chloride

windows.
Fill the cell with a mineral transformer oil w
...

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